Layered clay minerals such as montmorillonite are composed of silicate layers with a thickness on a nanometer scale (1 nanometer=10 Å). Dispersions of such layered materials in polymers are frequently referred to as nanocomposites.
It is known that silicates such as smectite clays, e.g., sodium and calcium montmorillonite, can be treated with various types of swelling agents such as organic ammonium ions, to intercalate the swelling agent molecules between adjacent, planar silicate layers, thereby substantially increasing the interlayer spacing. The intercalated silicates can then be exfoliated, i.e., the silicate layers are separated, typically by shear mixing. The individual silicate layers, when admixed with a matrix polymer before, after, or during the polymerization of the matrix polymer, have been found to substantially improve one or more properties of the polymer such as modulus and/or high temperature characteristics.
For example, U.S. published application 2001/0008699 discloses polymer/platelet multi-layer films in which the inner layer is composed of a carrier resin and platelet particles of a specific size. The platelets can be clay materials or non-clays. Dispersing aids such as alcohols and water-dispersible polymers can be present. U.S. Pat. No. 4,764,326 discloses a process for blending a polyolefin, prior to extrusion, with an extrusion processing aid comprising (a) an acid amide or alkylene bis-amide, (b) an aliphatic hydrocarbon or mixtures thereof, and (c) an oxygen-containing high density ethylene polymer such as oxidized polyethylene. Fillers such as an unspecified type of clay can also be present. U.S. Pat. No. 4,810,734 discloses a method for producing composite materials by contacting a layered clay mineral such as montmorillonite with a swelling agent in the presence of a dispersion medium to form a complex, mixing the complex with the monomer, and polymerizing the monomer in the mixture. Ethanol, ethylene glycol, glycerin, a mixture of water and dimethylformamide, and acetic acid are disclosed as suitable dispersion media.
Polyolefin nanocomposites generally make use of maleic anhydride-grafted polyolefins to compatibilize and disperse an organoclay in the polymer matrix. To achieve significant intercalation usually requires a minimum graft copolymer/organoclay ratio of 5:3; exfoliation requires a 10+:3 ratio. Since the graft copolymer and the organoclay are expensive materials, the above ratios have a significant impact on the cost of the finished product.
There is therefore a need for a cost-effective alternative to maleic anhydride-grafted polyolefins for producing nanocomposites with improved mechanical performance and barrier properties.